Celestron AVX polar align problems - SOLVED

[johngwheeler]

I've just bought a Celestron AVX mount, and and tried it the first time yesterday with a 6" Mak, and I've had some odd behaviour with the go-to & alignment features.

I started off with a 2-star alignment, choosing two visible stars (not far from the meridian) and then a calibration star in the West.

The Go-to features seemed to work well, except when I tried to go to the Moon. The mount missed it by about 30 degrees! I did a go-to to Saturn, and it was spot on. Any idea why this would be? My location and local time information seems to be correctly entered.

I also tried a polar alignment using my calibration star (Spica). The mount slews away from the target after centering it, but then go back to a point about 90 degrees away. I was expecting it to return to a point close to the star, and then asking me to adjust the mount to centre the star in the finder and eyepiece.

Is there some problem with my choice of alignment stars that has confused the alignment process?

I'll try again tonight with different stars, but I'd be interested in understanding what has happened!

Thanks for any advice you can give.

John.

[sil]

Balance/weight? I found my cgem dx was VERY fussy about balance and alignment accuracy. I also joined a beta celestron firmware group and firmware made a big difference too. My start setup was polar aligned and slewing to alignment stars from there was a problem like yours when I first got the scope, after beta firmware update it was good. With the 11" cas it was at its worst, if i swapped on a smaller lighter scope/load alignment would be reliable. Also make sure you're alignment stars are properly identified and your finderscope centers on whatever is centered in the eyepiece. I found balancing with the scope pointed at what i want to photograph helped. I'm sure the motor/power strain differs as the scope changes position and it doesn't take much to put things out.

Also some ideas on http://www.nexstarsite.com/OddsNEnds/ASGTRunaway.htm. Try get your balance as good as possible, use the longer alignment options available, I would go with more than 3 calibration stars, small time cost to do at the start of an imaging session. Also try to get firmware updates, the official celestron site seems to only have "final" firmwares that are years out of date, but the beta fimwares are available elsewhere and are stable enough to get rid of many issues (I think i got onto them through a post on Cloudy nights form, it was not a celestron url it took me too, might have been the nexstar site but cant recall from memory exactly. But it made my mount so much better and accurate, initial alignment were noticably more accurate and track much better too. There were a ton of fixes for southern hemisphere users.

[johngwheeler]

I finally found a way to update the firmware in my Celestron AVX mount after struggling in vain with non-functional drivers in the 9-pin Serial-to-USB adapter I bought from eBay - in the end I used an old laptop I had in the cupboard which I recalled had a serial port on it. (Hence justifying my tendency never to throw away old-tech :) )

This (combined with more careful choice of alignment stars) seems to have fixed my polar alignment problem.

[Camknox]

With the Celestron alignment routine they don't really mention it anywhere but for your 3 stars you should be following the triangle method;

Star 1 - Should be mid height somewhere in the south-eastern sky
Star 2 - Should be mid height somewhere in the northern sky
Star 3 - Should be mid height somewhere in the south-western sky

You will effectively have drawn a triangle around yourself giving the mount the best possible solution. Don't have the stars too close to the meridian and don't bother with anything near the SCP as the northern-hemisphere programmers don't like us much.

[johngwheeler]

Thanks for the suggestions. I've had quite good results (Aug 2015) with:

Alignment star 1: Promixa Centauri (Rigil Kent)
Alignment star 2: Spica
Calibration star 1: Alnair
Calibration star 2: Altair

The rule is that alignment and calibration stars should be in opposite meridians, not too close to the celestial pole or zenith, and separated by at least 45 degrees.

For polar alignment I'd use something close to north, between 30-60 degrees elevation, but sometimes this requires using one of the calibration stars if I can't correctly identify the dimmer stars!

[raymo]

Proxima Centauri is not Rigel Kent. Alpha Centauri is. Proxima is a long way from Alpha, and hard to find if you don't know exactly where to look.
raymo

[johngwheeler]

Oops! Yes, I knew that, but must have been thinking of something else when I wrote it. It does highlight the importance of accurately identifying and naming the alignment stars - otherwise you get into all sorts of grief!